U.S. patent number 7,053,344 [Application Number 09/889,843] was granted by the patent office on 2006-05-30 for self regulating flexible heater.
This patent grant is currently assigned to Illinois Tool Works Inc. Invention is credited to Edward Bulgajewski, by Antoinette Chiovatero, Fred A. Kish, James Surjan, Tilak R. Varma.
United States Patent |
7,053,344 |
Surjan , et al. |
May 30, 2006 |
Self regulating flexible heater
Abstract
A self-regulating flexible heater for automobiles and other
vehicles which is comprised of a breathable substrate (10) to which
is applied a coating (14) of a conductive material and a coating
(12) of positive temperature coefficient material.
Inventors: |
Surjan; James (St. Charles,
IL), Kish; Fred A. (Chicago, IL), Varma; Tilak R.
(Grayslake, IL), Bulgajewski; Edward (Genoa, IL),
Chiovatero; by Antoinette (legal representative, Chicago,
IL) |
Assignee: |
Illinois Tool Works Inc
(Glenview, IL)
|
Family
ID: |
36462604 |
Appl.
No.: |
09/889,843 |
Filed: |
January 24, 2000 |
PCT
Filed: |
January 24, 2000 |
PCT No.: |
PCT/US00/01702 |
371(c)(1),(2),(4) Date: |
July 22, 2002 |
PCT
Pub. No.: |
WO00/43225 |
PCT
Pub. Date: |
July 27, 2000 |
Current U.S.
Class: |
219/549; 219/528;
219/543; 219/529; 219/217 |
Current CPC
Class: |
H05B
3/34 (20130101); B60H 1/2227 (20190501); H05B
2203/006 (20130101); H05B 2203/011 (20130101); H05B
2203/017 (20130101); H05B 2203/02 (20130101); H05B
2203/029 (20130101); H05B 2203/013 (20130101) |
Current International
Class: |
H05B
3/54 (20060101) |
Field of
Search: |
;219/549,202,203,211,212,217,219,520,528,529,538,543,546,547,548,553,505
;392/425,432,435 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2000-333781 |
|
Dec 2000 |
|
JP |
|
2004-55219 |
|
Feb 2004 |
|
JP |
|
Primary Examiner: Bennett; Harry
Assistant Examiner: Patel; Nihir
Attorney, Agent or Firm: Croll; Mark W. Donovan; Paul F.
Claims
What is claimed is:
1. A self regulating flexible heater construction for producing
heat when connected to an electrical power source, comprising: a
flexible fabric substrate conformable to the shape of a contiguous
flexible surface to be heated; a layer of a positive temperature
coefficient material; and a layer of a conductive material, wherein
the fabric construction has a bulk density of about 0.6 g/cm.sup.3
or greater and a thermal diffusivity of about 0.003 cm.sup.2/s or
greater.
2. The heater of claim 1 wherein at least one of the layers is
applied to the heater in an interdigitated pattern.
3. The heater of claim 2 wherein the substrate is woven or
non-woven fabric.
4. The heater of claim 2 wherein the layer of conductive material
is applied to the layer of positive temperature coefficient
material in an interdigitated pattern.
5. The heater of claim 2 wherein the layer of positive temperature
coefficient material is applied to the layer of conductive material
in an interdigitated pattern.
6. The heater of claim 2 wherein the density of the fabric is 1 to
6 ounces per square yard.
7. The heater of claim 2 wherein the PTC material is comprised of a
polyolefin resin.
8. The heater of claim 2 wherein the coating of PTC material has a
weight 7 to 20 lbs. per ream.
9. The heater of claim 2 wherein the positive temperature
coefficient material has a surface resistivity of 2 to 10 kilo-ohms
as measured by multimeter probes set 1 cm apart.
10. The heater of claim 2 wherein the positive temperature
coefficient material has a surface resistivity of 3 to 8 kilo-ohms
as measured by multimeter probes set 1 cm apart.
11. The heater of claim 2 wherein the conductive material is
formulated from a mixture of a polymeric resin selected from the
group consisting of vinyls, polyesters, acrylics and a conductive
material selected from the group consisting of silver pigment, a
silver coated copper pigment, or plated copper pigments.
12. The heater of claim 2 wherein the conductive material is
formulated from a mixture of solvating materials selected from the
group consisting of organic solvents and water based solvents and a
conductive material selected from the group consisting of silver
pigment, a silver coated pigment, or plated copper pigments.
13. The heater of claim 2 wherein the conductive material is
constructed of conductive wires fixed within the construction by
conductive glues.
14. The heater of claim 1 wherein at least the layer of conductive
material is applied tothe substrate by screen printing, spraying,
draw down, web printing or any other printing method capable of
providing a uniform coating.
15. The heater of claim 1 further comprising a plurality of buss
bars in electrical contact with the conductive material and an
electrical power source.
16. The heater of claim 15 wherein the buss bars have a width
dimension and a length dimension, and wherein the width decreases
over at least a portion of its length.
17. The heater of claim 15 wherein the buss bars have a width
dimension and a length dimension, and wherein the width remains
constant over at least a portion of its length.
18. The heater of claim 15 wherein the buss bars have a width
dimension and a length dimension, and at least one void at a
preselected location along its length.
19. The heater of claim 15 wherein the buss bars have a width
dimension and a length dimension, and wherein the width dimension
increases step-wise over at least a portion of its length.
20. The heater of claim 15 wherein the spacing of the busses varies
across the heater.
21. The hearter of claim 2 further comprised of an overlayer of a
laminated or sewn secondary breathable woven or non-woven fabric
comprised of natural or synthetic fibers which covers the
heater.
22. A self regulating flexible heater construction for producing
heat when connected to an electrical power source, comprising: a
flexible fabric substrate conformable to the shape of a contiguous
flexible surface to be heated; a layer of a positive temperature
coefficient material; a layer of a conductive material, wherein at
least one of the layers is applied to the heater in an
interdigitated pattern; an overlayer of a laminated or sewn
secondary breathable woven or non-woven fabric comprised of natural
or synthetic fibers which covers the heater, wherein the overlayer
is an encapsulating coating, which may be a flame retardant
coating, which is applied over the heater; and wherein the heater
is incorporated within the construction of a seat for an
automobile.
23. A self regulating flexible heater construction for producing
heat when connected to an electrical power source, comprising: a
flexible fabric substrate conformable to the shape of a contiguous
flexible surface to be heated; a layer of positive temperature
coefficient material; and a layer of conductive material, wherein
the heater has a multiple buss design providing for high and low
current settings, comprised of at least a common setting buss, a
low setting buss, and a high setting buss, in which current flows
from either the common setting buss to high setting buss or from
the common setting buss to low setting buss.
24. The heater of claim 1 wherein the fabric construction includes
the flexible fabric substrate and the layer of positive temperature
coefficient material.
Description
FIELD OF THE INVENTION
The invention relates to a self-regulating flexible heater
construction suited for use in automobile components but which has
use in other applications, including but not limited to furniture
pieces, consumer items, construction materials, and other articles.
The flexible heater construction is comprised of a breathable
fabric substrate to which is applied a coating of a conductive
material and a coating of positive temperature coefficient ("PTC")
material. The conductive material is in electrical contact with a
power source. The PTC material regulates the temperature of the
heater.
Within the automotive field, the present invention can be employed
as a seat heater and to provide a non-exhaustive list of other
applications, as a heater for dashboards, steering wheels, stick
shifts (for manual and automatic transmissions), mirrors, arm
rests, and others.
BACKGROUND OF THE INVENTION
Heating devices with temperature self-regulating properties are
used in the automotive industry. However, such heaters are employed
where flexibility of the heater is not at issue. For example, such
heaters are used on mirrors located outside of the vehicle. These
heaters are printed upon a rigid biaxially oriented polyester film.
See, e.g. U.S. Pat. Nos. 4,931,627 and 4,857,711, both assigned to
the assignee of the present application.
Heaters for automotive vehicle seats that are currently available
offer less than adequate performance due to several undesirable
attributes. Current heaters are known to build up static
electricity, which damages the heater controller circuit when it is
discharged. Another shortcoming is that current seat heater design,
in which the heater elements are copper wire and design creates
several problems in that heating is localized to the area of the
wires, creating an undesirable heating pattern where the areas in
the vicinity of the wire are too hot and areas removed from the
wire are too cool. Moreover, since the heating wire per se does not
possess any means for regulating the temperature (that is, copper
wire and the like is incapable of sensing that it has become too
hot), a sophisticated temperature controller is required for
regulating the temperature of the seat heater. This creates a
challenging design problem for the engineer, which could be avoided
if the heater construction per se was self-regulating and could
increase or decrease the amount of heat produced as necessary.
Furthermore, when heating a seat in an automotive vehicle, it is
evident that the seat heater construction must be flexible,
durable, and able to withstand the demands of the operating
environment, which include the potentially degradative effects of
prolonged exposure to heat and the flow of electricity.
It would be desirable if a heater for an automotive seat were
deigned so that a uniform amount of heat could be distributed over
the area to be heated. Likewise it would be desirable if a seat
heater could be designed in which, if desired, the amount of heat
delivered to particular area could be varied as a design parameter,
so that if it is deemed that certain areas should be warmer than
others for a given design (or cooler, as the case may be), the
heater could be constructed to accommodate this variation.
Furthermore, since the comfort of a vehicle seat is attributable to
its flexibility, it would be desirable if the seat heater
construction was flexible so that its presence in the seat
complimented the other flexible components of the seat
construction. It would be additionally desirable if the seat heater
construction incorporated a flexible fabric layer. It would be
highly advantageous if the heater components could be applied to
the fabric using well known printing and coating techniques, which
could be used to construct a heater quickly and easily, and
relatively cheaply. Also, application techniques such as printing
or coating could be used to make uniform or varying applications of
component materials, which could provide for the uniform
distribution of heat, or if desired, variations in the amount of
heat.
Positive temperature coefficient (PTC) materials exhibit variable
electrical resistance with temperature. As the temperature of the
material increases, the electrical resistance also increases. The
resistivity of the material increases so current flow is reduced,
limiting heat flow. In essence, positive temperature coefficient
compositions are used to form temperature self-regulating coatings.
PTC materials are known in the art. Exemplary disclosures
concerning these materials can be found in U.S. Pat. Nos. 5,206,482
and 5,151,747, among others.
SUMMARY OF THE INVENTION
The present invention is directed to a self regulating flexible
heater, such as a heater for use in automobiles and other vehicles,
in which a PTC material and conductive material are applied to a
woven or non-woven fabric that is constructed of natural or
synthetic fibers.
An electrical buss system of a conductive material is applied over
a fabric before or after being coated with a PTC material. The
conductive material is applied in an interdigitating pattern
emanating from multiple buss bars. The buss bars are configured
such that the heater offers uniform heating across the surface of
the heater. The amount of heat generated may also be varied as a
design parameter so that certain regions generate more or less heat
as desired. The buss bars can be connected to the power source by a
variety of interconnection devices such as fasteners, terminals
conductive epoxies, to name a few of a broad range of
interconnecting means that would be within the realm of the skilled
artisan. Wire connectors are attached to the terminals and the wire
from the power source. Preferably, a secondary layer is applied
over the heater construction, such as an adhesive layer or a
breathable fabric. The breathable fabric may be one that is
breathable by virtue of the material that is used, or one that is
machined to be breathable, such as by needle punching.
The heater element is applied just under the external layer of the
vehicle seat, preferably as close to the end user as possible. The
heater element is placed on the base of the seat, or on the back of
the seat, or both. Preferably, the coating of PTC material has a
weight 7 to 20 lbs per ream (that is, 3300 ft..sup.2) and a surface
resistivity of 2 to 10 kilo-ohms as measured by mulitimeter probes
set 1 cm apart. More preferably the coating of PTC material has a
surface resistivity of 3 to 8 kilo-ohms as measured by mulitimeter
probes set 1 cm apart.
Suitable materials for the fabric substrate include woven and
non-woven fabric constructions of material including but not
limited to polyesters, polyamides, polyaramids, polyimides,
polyetherketones, glass fibers, phenolics, and carbon fibers. With
respect to the fabric selection process, it has been found that
heater constructions having a bulk density of about 0.6 g/cm.sup.3
or greater and a thermal diffusivity of about 0.003 cm.sup.2/s or
greater insures a desirable degree of conductivity and heat flow
through the fabric. This can be achieved using multifilaments with
a relatively high number of twists per inch. However, a high degree
of twists, or even using high denier fibers, reduces fabric
flexibility. Accordingly, the skilled artisan should strike a
balance between these properties.
The heating element may comprise a coating formed from a
composition of a conductive material of electrically conductive
particles dispersed in a polymer matrix, and a coating of a PTC
material. In the self-regulating heater of the present invention,
the heating element is in thermal communication with the component
to be heated, such as the automobile seat. Preferably, the PTC
material is coated onto a woven or non-woven fabric. The conductive
material is applied, either before or after the PTC material is
applied. The conductive material is coated onto the fabric in an
interdigitating pattern of electrodes which forms an electrical
buss system, which can be constructed in a variety of patterns,
such as in a tapered shape (see e.g., FIG. 1), a stepped shaped, in
which size varies in a step arrangement, or in a straight, or
constant size over the entire construction. (see e.g., FIG. 3) A
trim pattern is also possible in which voids are present in the
busses at preselected locations. The edges of the buss system are
connected to multiple buss bars in electrical contact with a power
source.
In one aspect of the present invention, the self-regulating
flexible heater is a coated fabric whose construction has a bulk
density of about 0.6 g/cm.sup.3 or greater and a thermal
diffusivity of about 0.003 cm.sup.2/s.
In another aspect of the invention, an encapsulating coating, which
may be a flame retardant coating, is applied over the heater
elements by lamination or the or other known techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view showing the heater of the present
invention.
FIG. 2 is a top plan view of the circuit of a dual wattage
self-regulating flexible heater construction.
FIG. 3 is a top plan view of a self-regulating flexible heater
construction having a tapered and straight buss bar
arrangement.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the preferred embodiment, a polyester woven or non-woven fabric
10 of a density of about 1 to 6 ounces per square yard (more
preferably, about 3.7 ounces per square yard) is coated with a PTC
material 12 such as commercially available PTC coating materials,
such as an ethylene-vinyl acetate co-polymer resin available as
Dupont 265. Such materials are described in U.S. Pat. No.
4,857,711, incorporated herein by reference. The coating is applied
at a weight of 13 lb per ream (that is, 3300 ft..sup.2) and
resistivity of 2 to 10 kilo-ohms (more preferably, 3 to 8
kilo-ohms) as measured by mulitimeter probes set 1 cm apart.
Prior to application of the conductive material, the fabric is
fully dried. The PTC layer 12 and conductive layer 14 are applied
as discreet layers in any order of application. The conductive
material 14 may be formulated from polymeric resins such as vinyls,
polyesters, acrylics and conductive material such as silver
pigment, a silver coated copper pigment, or plated copper pigments
and/or solvating materials such as organic solvents, and
water-based solvents which contain the conductive material. After
thorough mixing, the coating is passed through a mill to effect
final dispersion. Other conductive materials may be used such as
conductive woven wires fixed within the construction by conductive
glues. The applicants have found that these formulations are
flexible while resisting cracking when bearing a load and when
stretched.
The conductive material 14 is preferably applied in an
interdigitating pattern (see FIG. 1) by a screen printing method,
then fully dried, thereby forming an electrical buss system. Other
methods may be used to apply the conductive material, including
spraying, draw down applications, web printing, or other printing
methods that provide a uniform coating. The conductive material is
printed in electrode patterns which are interdigitated. Each
electrode of the pattern is in electrical contact with one of a
multiple of buss bars 16 and 18, with adjacent electrodes
alternating their connection between buss bars 16 and 18. The buss
bars are configured in a decreasingly tapered arrangement. That is
the width of the buss bars gradually decreases from the terminal
end (20, 22) to the free end (24, 26). This insures that the
electrical resistance created by the buss bars will create a
heating effect that is substantially the same as that created by
the heating areas. One knowing the electrical characteristics of
the PTC material, conductive material and temperature requirements
can readily design heating areas of varying sizes and shapes with
varying buss sizes that can deliver varying amounts of heat over
the heating area. Accordingly, the entire substrate, from the
center out of the periphery, including those areas beneath the buss
bars, will be heated as desired with substantially no cold spots.
It should be noted that while the connections to the heater
construction are positioned along its edges, other configurations
are possible, such as making a connections from the interior of the
construction, or a combination of connections along the edges and
in the interior.
Power across the heater construction can be varied by varying the
spacing of the smaller busses, That is, the skilled artisan would
readily appreciate that doing so would vary the power at any given
location in the construction.
FIG. 2 shows a circuit diagram for a self-regulating flexible
heater design in accordance with the present invention which
provides for a multiple wattage heater. As shown in this design,
high/low settings are possible where current flows from either
common to high buss arrangement or a common to low buss
arrangement. Other combinations are possible based on other
terminal connections.
Terminals 20 and 22 are attached to the buss bars and are in
communication with a power source (not shown). The terminals may be
attached to the buss bars 16 and 18 by fasteners or any other means
that will permit an electrical contact to be formed. A secondary
protective layer, such as an encapsulating layer, may be laminated
over the heater assembly 30.
When a voltage is applied across the terminals and across the
electrode array, depending upon the ambient temperature and the
electrical characteristics of the PTC material, current will flow
through the PTC material between the electrodes, generating heat in
the individual heating areas. The current flow and heating effect
of the PTC material depends on its temperature which will change as
the ambient temperature changes and, at a predetermined temperature
of the PTC material, the resistivity of the material increases
causing the material to no longer conduct current, whereby the
heating areas no longer generate heat, or to produce a very low
amount of heat due to a significantly reduced current flow.
Accordingly, it can be seen that the heater is self-regulating in
accordance with the surrounding ambient temperature.
FIG. 3 depicts an alternative arrangement in which the width of the
buss bars is a combination of a section where the size remains
constant near the free end (24, 26), and a tapered section where
the buss bars gradually decrease in size further away from the
terminal end (20, 22).
The skilled artisan will readily appreciate that placing a safety
switch at the terminals will prevent run away conditions during
which the heat generated exceeds the upper limit that has been set
in the design of the heater. The switch can be a simple on-off
switch that permits the user to turn off the current flowing
through the heater.
EXAMPLE 1
The thermal diffusivity of five coated polyester fabric sample was
determined.
The samples, identified as 1 through 5, differed in terms of the
whether they are woven or non-woven, and if woven, the weave
pattern, number of picks per inch, ends per inch, number of
filaments in the warp and filling yarns, and twists per inch in the
yarns. These fabrics were submitted as strips of coated fabric
approximately 500 mm long by 70 mm wide. Samples 12.7 mm in
diameter were die cut from the strips for testing.
Thermal diffusivity of the samples was measured att 10.degree. and
100.degree. by the laser flash method utilizing a Holometrix
Microflash instrument available from Holometrix Micromet. This
instrument and method conform to ASTM E1461-92, "Standard Test
Method for Thermal Diffusivity of Solids by the Flash Method". The
test results are given after a description of the experimental
procedure.
Thermal diffusivity is related to the steady-state thermal
conductivity through the equation .lamda..times. .times..rho.
##EQU00001## where D is the thermal diffusivity, .lamda. is the
thermal conductivity, C.sub.p is the specific heat, and .rho. is
the density. The diffusivity is a measure of how quickly a body can
change its temperature; it increases with the ability of a body to
conduct heat (.lamda.) and it decreases with the amount of heat
needed to change the temperature of a body (C.sub.p). All three
quantities on the right hand side of Equation (1), as well as the
thermal diffusivity, can be functions of temperature.
The measurement of the thermal diffusivity of a material is usually
carried out by rapidly heating one side of a sample and measuring
the temperature rise curve on the opposite side. The time that it
takes for the heat to travel through the sample and cause the
temperature to rise on the rear face can be used to measure the
through-plane diffusivity and calculate the through-plane thermal
conductivity if the specific heat and density are known.
Through-Plane Method and Analysis
The sample is a disk with a standard diameter of 12.7 mm and a
thickness ranging from about 0.1 to 3 mm. With the Holometrix
Thermaflash 2200 Laser Flash system, the sample disk is aligned
between a neodymium glass laser (1.06 .mu.m wavelength 330 .mu.s
pulse width) and an indium antimonide (InSb) IR detector in a
tantalum tube furnace. A type C thermocouple in contact with the
sample controls the sample and its surroundings at any temperature
between 20 and 2000.degree. C. Once the sample has been stabilized
at the desired temperature, the laser is fired several times over a
span of a few minutes and the necessary data is recorded for each
laser "shot". The laser beam energy strikes and is absorbed by the
front surface of the sample, causing a heat pulse to travel through
the thickness of the sample. The resulting sample temperature rise
is fairly small, ranging from about 0.5 to 2 degrees C. This
temperature rise is kept in the optimum range by adjustable filters
between the laser and the furnace. A lens focuses the back surface
image of the sample onto the detector and the temperature rise
signal vs. time is amplified and recorded with a high speed A/D
converter.
Conductivity
The sample thermal conductivity can be calculated with Equation
(1), after a measurement of the diffusivity as described above, and
with measurements of the sample specific heat and bulk density. The
bulk density is normally calculated from the measured sample volume
(calculated from the measured dimensions) and mass.
Test Results
The measured values of thickness, bulk density and thermal
diffusivity are given in table 1 below. The results have not been
corrected for thermal expansion. The samples were coated with
approximately 5 .mu.m of graphite for thermal diffusivity testing.
The second column from the right in Table 1 lists the standard
deviation as a percentage of the mean diffusivity for the five to
ten laser "shots" taken for each data point. The bulk density
values are estimated to be accurate to within .+-.5%.
TABLE-US-00001 TABLE 1 Laser Flash Thermal Diffusivity Results Bulk
Temper- Thermal Thickness @ Density @ ature Diffusivity 25.degree.
C. 25.degree. C. Tested .alpha. Fabric Sample (mm) (g/cm.sup.3)
(.degree. C.) (cm.sup.2/s) Type 1 0.288 0.634 10 0.00360 B-3 100
0.00297 Polyester 2 0.180 0.555 10 0.00647 B-2 100 0.00562
Polyester 3 0.220 0.677 10 0.00617 IFC 322-222 100 0.00505
Polyester 4 0.269 0.510 10 0.00242 non- 100 0.00205 Woven Polyester
5 0.556 0.910 10 0.00255 PUR 100 0.00203 Coated Polyester Note:
Thermal Diffusivities are an average of 5 readings.
EXAMPLE 2
The five polyester test samples discussed in example 1 were tested
to determine if they would break down when subjected to extended
period of operation. The samples were coated with PTC material.
After drying a silver pigment was applied on top of the PTC
material. These self-regulating flexible heater constructions were
subjected to a 12 volt DC potential for an extended, continuous
period. Heat continued to rise in the constructions, until steady
state was attained for construction nos. 1 and 3. These
constructions exhibited sufficient heat resistance. Constructions
2, 4 and 5 were destroyed before reaching steady state. That is,
the "failed" heater constructions burned up during testing as a
result of heat generated during heater operation. It is noted that
the fabrics which passed exhibited a bulk density of at least about
0.6 g/cm.sup.3 or greater and a thermal diffusivity of at least
about 0.003 cm.sup.2/s.
TABLE-US-00002 Laser Flash Thermal Diffusivity Results Bulk Thermal
Thickness @ Density Temperature Diffusivity Heater 25.degree. C.
25.degree. C. Tested .alpha. Fabric Construction Sample (mm)
(g/cm.sup.3) (.degree. C.) (cm.sup.2/s) Type Pass/Fail 1 0.288
0.634 10 0.00360 B-3 Barely 100 0.00297 Polyester Passed 2 0.180
0.555 10 0.00647 B-2 Failed 100 0.00562 Polyester 3 0.220 0.677 10
0.00617 IFC 322-222 Passed 100 0.00505 Polyester 4 0269 0.510 10
0.00242 non- Failed 100 0.00205 Woven Polyester 5 0.556 0.910 10
0.00255 PUR Failed 100 0.00203 Coated Polyester Note: Thermal
Diffusivities are an average of 5 readings.
With respect to the fabric selection process, it has been found
that heater constructions having a bulk density of about 0.6
g/cm.sup.3 or greater and a thermal diffusivity of about 0.003
cm.sup.2/s or greater insures a desirable degree of conductivity
and heat flow through the fabric. This can be achieved using
multifilaments with a relatively high number of twists per inch.
However, a high degree of twists, or even using high denier fibers,
reduces fabric flexibility. Accordingly, the skilled artisan should
strike a balance between these properties.
Though described in its preferred embodiment as a seat heater for
automobiles, it should be understood that the self-regulating
flexible heater construction of the present invention is suited for
use not only in automobile components but has use in other
applications, including but not limited to furniture pieces,
consumer items, construction materials, and other articles.
Accordingly, the preceding disclosure should be read as providing
context to the invention, and not as a limitation on the field of
use thereof.
Having described the preferred construction of the invention, those
skilled in the art having the benefit of the description, can
readily devise other modifications and such other modifications are
to be considered to be within the scope of the appended claims.
* * * * *